Alkyd resins are long-established binder polymers for film-forming coating compositions acknowledged for their esthetic properties, low surface tension (which enables the wetting of and adhesion on a wide variety of substrates and facilitates pigment wetting), applicability by various techniques, and cost-effectiveness. Because of these properties, alkyd resins are the most widely used air drying binders in coating compositions. Alkyd resins comprise drying or semi-drying unsaturated fatty acids or oils, which are generally attached to the polyester backbone of polyols and polycarboxylic acids. When the coating composition is applied to a substrate, the drying process starts by solvent evaporation and the binder polymers undergo autoxidation and subsequently form cross-links between the polymer chains resulting in a solid and coherently dried film. The drying process of autoxidizable architectural coating compositions takes place at ambient temperatures ranging from −10 to 50° C., whereby the presence of oxygen is essential. Generally, the drying process proceeds slowly.
Amine components such as polyaspartic acids have first been introduced in the early 1990s. This technology was initially used in conventional 2K polyurethane resins as reactive diluents to reduce the VOC-content. The chemistry of polyaspartic coatings is based on a reaction of a polyisocyanate with a polyaspartate. Polyfunctional amine components have been used as coreactants for isocyanates in many applications. Their use in coatings, however, has been limited due to their very high reactivity. Typical primary and secondary amine based systems are characterized by very short gel times, resulting in a short or no pot life and aesthetically deprived films, due to restricted flow and leveling. Polyaspartic esters exhibit a reduced reactivity towards polyisocyanate compounds compared to typical primary and secondary polyamines. The unique structural feature of the polyaspartic ester is a sterically crowded environment around the nitrogen. Additionally, the ester portion of the structure provides inductive effects. These features both act to slow down the reaction of the amino group of the polyaspartic ester compound and the isocyanate group of a polyisocyanate.
However, because of the low intrinsic viscosity of polyaspartics and the poor response to thickening agents, the difficulty to matt, the high cross linking density which makes the film hard and less flexible for non-dimensional stable substrates, the incompatibly to alkyd colorants and the high price, there exists a need to improve the performance of coating compositions that comprise polyaspartic resins. It is accordingly one of the objects of the present invention to overcome or ameliorate at least one of the disadvantages of the prior art.